In about ⅔ cases of primary breast cancer cases, estrogen receptor (ER) is present in breast cancer cells (referred to as “ER-positive”). In ER-positive breast cancer cells, binding of estrogen to ER contributes to cell proliferation.
Therefore, in the treatment for node-negative and ER-positive breast cancer patients, hormonal therapy targeting ER plays an important role.
In hormonal therapy for the node-negative and ER-positive breast cancer patients, metastasis of breast cancer and recurrence are suppressed by, for example, administering an antiestrogen such as tamoxifen to the patients, thereby blocking the binding of estrogen to ER in the breast cancer cells to suppress proliferation of breast cancer cells. In the case where the above patients are treated with the above hormonal therapy, most of the patients show comparatively good prognosis.
However, about 20% of the above patients may have a recurrence of breast cancer.
Therefore, in order to reduce the recurrence rate, most of the node-negative and ER-positive breast cancer patients are treated with not only hormonal therapy but also adjuvant chemotherapy at present, even though chemotherapy is considered to be unnecessary for the node-negative and ER-positive breast cancer patients in most cases.
Thus, it seems to be important to predict the prognosis of the node-negative and ER-positive breast cancer patients in order to provide adjuvant chemotherapy only to patients who are at high risk for recurrence.
Recently, based on an analysis of comprehensive gene expression profile, prediction of breast cancer prognosis in a breast cancer patient has been attempted (see, for example, Patent Literatures 1 and 2, Non Patent Literature 1 and the like).
The Patent Literature 1 describes a method for classifying a breast cancer patient into a patient having “no distant metastases within five years from the time of initial diagnosis” or a patient having “distant metastases within five years from the time of initial diagnosis”, using gene markers identified by using tumor samples of 117 breast cancer patients, based on the difference between the gene marker expression in a cell sample of a breast cancer patient and the gene marker expression in a control. In addition, the Patent Literature 1 describes that as the gene markers, a gene marker capable of distinguishing the presence or absence of ER, a gene marker capable of distinguishing between tumors having a mutation of BRCA1 gene and sporadic tumors, and a gene marker capable of distinguishing between a patient having “no distant metastases within five years from the time of initial diagnosis” and a patient having “distant metastases within five years from the time of initial diagnosis” are used.
In addition, the Patent Literature 2 describes a method for diagnosing prognosis, comprising the steps of obtaining gene expression profile in the biological samples of breast cancer patients, with the use of 76 genes providing an indication of prognosis, the genes being identified by using tumor samples of 286 node-negative breast cancer patients, and comparing the expression level obtained from the gene expression profile with the predetermined cut-off levels.
Furthermore, the Non Patent Literature 1 describes a method for predicting a prognosis, wherein cases of breast cancer conventionally classified as histological grade 2 is further classified into a high-risk group for recurrence and a low-risk group for recurrence by using Genomic Grade Index (GGI) based on 97 genes, the genes being identified by using 189 cases of invasive breast cancer patients and three known gene expression datasets of breast cancer.